Taillight lenses for the '70-72 LeMans wagon are extremely hard to find. Have been for the last 15 years. As a longtime restorer/collector/vendor that travels and still boneyards, and am hardcore into '70-72's, can relate there are a few '70-72 wagons still out there in the country yards that rarely crush. Their tail light lenses were typically the first pieces to be sold. Personally have pulled and sold nearly a dozen singles over the years, most were pulled in the mid '80's-late 90's. Have been fortunate to get into several old dealership parts buyouts, such large '60's-70's dealership parts stock deals are near non existant anymore. Having worked hundreds iof swap meets including POCI & GTOAA Nat's, many times, along with monster meets like Spring Carlisle, the old Pate, seriously doubt such NOS lenses will appear at any local swappers.
As Jim mentioned, you're better off subscribing to POCI Smoke and running a want ad. Would also join the Performance Years forum (max performance) and run a wanted ad. The PY forum has a mass readership. If near OH in early August, it would be worth walking the swap meet at Norwalk and striking up a repoire with, and leaving a card with many of the more organized swapper vendors. Dont be surprised to be asked $75-100 apiece on used lenses. Good luck with your search!